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Rana sylvatica. Photo by E Zimmreman  

The Wood Frog can survive in the Artic by producing its own antifreeze. More...

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In 1773, Benjamin Franklin wrote “I wish it were possible... to invent a method of embalming drowned persons, in such a manner that they might be recalled to life at any period, however distant; for having a very ardent desire to see and observe the state of America a hundred years hence.”  He said he would prefer to be immersed in a cask of wine with a few friends, “then to be recalled to life by the solar warmth of my dear country!”  In 1941, science fiction author Robert Heinlein wrote about using “cold-sleep” to save space and reduce boredom during long space voyages.  By 1967, scientists were experimenting with humans and cryonics. Cryonics is the process of cooling a dead body to sub-zero temperatures in the hope of future resuscitation. (This is sometimes erroneously referred to as cryogenics, which is really a branch of physics that deals with super low temperatures.)

Wood Frog in Poconos, PA.  Photo by Bet Zimmerman.

But research shows that some frogs and turtles already have cryonics figured out, and they don’t have to die first.  One species of freezing frog - the Wood Frog (Rana sylvatica) - even does its thing right here in Connecticut.  As the world around it chills and ice touches its skin, this frog’s heart flatlines, blood stops flowing, the kidney stops functioning, and breathing comes to a complete halt.  It then freezes so stiff you could snap it in half (but please don’t!)  It can survive a body temperature down to 21°F for 2-3 months.  When spring arrives, the Frogsicle thaws from the inside out, and within hours resumes amphibian life. 

When normal organisms like humans are exposed to freezing temperatures, ice crystals form in blood vessels and cells, and membranes fail, resulting in frostbite or death.  But Wood Frogs manufacture their own form of antifreeze. When temperatures drop, their liver cranks out glucose (blood sugar).  The glucose circulates into the cells to prevent damage, while 65-70% of the water migrates out to form a puddle just under the skin, which then turns to solid ice.  

You can see why Wood Frogs are the only frog found north of the Arctic Circle.  They are tan, about 1 3/8 – 3 ¾” inches long, with a dark eye mask and creamy white belly. They make a raspy, duck-like quack. Wood Frogs breed primarily in seasonal wetlands called vernal pools.  These temporary pools are key to the life cycle of many amphibians, because they are too shallow to support fish that would eat their eggs or larvae. Wood Frogs also depend on landscape connectivity, since they go upland to hibernate, where they burrow down into a shallow depression underneath dead vegetation (called duff) to wait out the winter.

Wood frogs mating. Photo by Jean Pillo
Wood Frogs mating. Notice egg mass below. Photo by Jean Pillo.

Within a couple of days of defrosting, Wood Frogs start courting and mating. The male will tackle pretty much anything that moves, including a turtle’s head. The only way he knows whether he’s found a fertile female is by perching on her back and embracing her.  If the female is too thin, he knows it’s either another male, or a female that already dumped her eggs. Once he finds a firm, fat female, he hangs on for days until she lays her eggs, numbering about one thousand, which he then fertilizes. Hundreds of females may lay their eggs in a single gargantuan gelatinous egg mass on vegetation in shallow water in the vernal pool.


Originally published in The Woodstock Villager on 01/12/07. Photos by Bet Zimmerman.

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